Studies indicate that cholesterol-lowering 3-hydroxy 3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors ("statins") have immunomodulatory properties that may be beneficial in treatment of Th1-mediated autoimmune diseases. Oral atorvastatin (Lipitor) could either prevent or reverse ongoing relapsing or chronic EAE. Atorvastatin treatment induced a Th2 bias that was associated with STAT6 phosphorylation, and promoted differentiation of Th2 cells that adoptively transferred protection to untreated mice. EAE protection persisted after atorvastatin was discontinued, suggesting that atorvastatin treatment induced sustained immunomodulation (tolerance). Mevalonic acid, the product of HMG-CoA reductase, prevented both atorvastatin-induced Th2 differentiation by Th0 cells. The mevalonate pathway involves sequences of enzymatic reactions with branches that lead to the production of different isoprenoid compounds including dolichols, ubiquinone and cholesterol, as well as the postranslation modification (isoprenylation) of small GTP binding proteins (e.g. ras) involved in signal transduction. Thus, the mevalonate pathway is crucial for cell cycle progression and differentiation. We hypothesize that isoprenoid metabolites are necessary for Thl differentiation and that statins mediate Th2 differentiation by inhibiting production of specific mevalonate metabolites. We hypothesize that atorvastatin-induced Th2 cells will mediate bystander suppression. We propose to investigate the role of certain atorvastatin-induced regulatory cytokines in EAE protection. These studies will elucidate the mechanisms involved in atorvastatin-induced immunomodulation and role of the mevalonate pathway in T cell differentiation and regulation. The Specific Aims are: (1) To identify which metabolites in the branched mevalonate pathway influence T cell activation and differentiation and examine how atorvastatin and other selective inhibitors in isoprenoid metabolism influence signaling and gene transcription during T cell differentiation. (2) Gene microarray will be used to identify additional targets in immunodulation that may be altered by atorvastatin. (3) We will examine whether atorvastatin treatment induces bystander suppression, prevents epitope spreading of T cells and, using autoantigen microarray, inhibits spreading of antibodies. These studies have direct and immediate applicability to the use of statins in treatment of autoimmune disease.